As a class of semiconducting device to transform detected light into electrical signal, photodetectors are of great importance for a variety of applications, such as image sensing, data communication, remote control and so forth. Currently, the commercially available active materials for photodetectors are mainly based on inorganic semiconducting materials, such as ZnO, Si, GaAs and PbS. These materials typically have detectivity greater than 1012 Jones but suffer from high expense and relatively rigor working conditions (e.g., GaAs detectors have to work at very low temperature). In addition, these inorganic materials are fragile, non-foldable and have low malleability, limiting their applications in novel and high-demanding fields. Therefore, alternatives to such commercial materials are expected and necessary regarding the merits of low-cost, mild working conditions, and novel characteristics, such as flexibility and semitransparency.
Conjugated polymers have attracted broad interest from academy and industry as a new class of emiconductor due to their advantages of low-cost, simple processing, flexibility and semi-transparency. High external efficiency, fast response, and detection to near infrared (NIR) range (1450 nm) have been demonstrated in polymer photodetectors. Besides, they are suitable for large area detection and could be operated at room temperature and flexible substrates, affording new opportunities for sensing and detecting technologies. Similar to that of polymer solar cells, bulk heterojunction structure is employed to construct polymer photodetectors, with conjugated polymer as the electron donor and fullerene derivative as the electron acceptor. It favors photon absorption and charge separation, affording high external quantum efficiency. However, it usually generates a relative high dark current density at negative bias and low rectification ratio between forward/reverse bias, remaining difficult to achieve high detectivity over the broad spectral range from ultraviolet (UV) to NIR. There are many strategies to develop new polymer photodetectors with high detectivity including interfacial engineering, morphology control of the active layer, and improvement of structure, but few works reported are related to molecular structure design.